Naphtha treating process



May 12, 1959 E. R. cHRlsTENsEN ETAL 2,886,509y

NAPHTHA TREATING PROCESS Filed OCb. 17, 1955 United States NAPH'IHA TREATWG PROCESS Application October 17, 1955, Serial No. 540,878

3 Claims. (Cl. 208-91) This invention relates to a process for the treatment and conversion of petroleum fractions. More particularly, the invention relates to the treatment of light naphthas boiling in the range 40-225" F., more or less, and containing straight chain and non-straight chain hydrocarbons, such as light straight run naphthas and light catalytic reformed (Platformate) naphthas.

Light naphthas are generally characterized by having relatively low octane numbers. This is due to the high proportion of low octane normal parains, such as npentane, n-hexane and n-heptane, in such naphthas. Because of their relatively low octane number, light naphthas are not well suited for blending in high octane fuels.

Various processes have been proposed for upgrading or improving the octane rating of light naphthas. Generally, these processes have as a major purpose the conversion of low octane straight chain hydrocarbons (n` arent G parains) into branched chain or cyclic hydrocarbons l which have substantially higher octane ratings. conversions are quite difiicult, however, due to the refractory nature of the relatively low molecular weight, C9 and lower, straight chain hydrocarbons. The low molecular weight straight chain hydrocarbons may be converted to higher octane branched or cyclic hydrocarbons only under relatively severe treating conditions. Under certain conditions suitable for the conversion of straight chain hydrocarbons to non-straight chain cyclic hydrocarbons the straight chain hydrocarbons are subject to cracking with resultant formation of gas (methane, ethane and propane) and carbon. The formation of gas and carbon during these treating processes substantially reduces the amount of liquid hydrocarbons recoverable and therefore adversely aects the commercial attractiveness of such processes.

A principal object of this invention is to provide an irnproved hydrocarbon conversion process. Another object vis to provide a process for the conversion of hydrocarbon fractions containing substantial amounts of straight chain hydrocarbons. Still another object is to provide a process for upgrading light naphthas boiling in the range 40-225 F., and containing a substantial amount of straight chain hydrocarbons. A further object is to provide a process wherein the normal parain content of light naphthas is converted to higher octane products in aschemeeffective to substantially eliminate straight chain hydrocarbons from the linal product. How these and other objects of the invention may be accomplished will become more obvious from the accompanying detailed description and the drawing which schematically illustrates an embodiment of the practice of this invention.

In accordance with our invention, a light naphtha is contacted with a solid adsorbent, which selectively adsorbs straight chain hydrocarbons to the substantial eX- clusion of non-straight chain hydrocarbons, to adsorb straight chain hydrocarbons from said naphtha followed by desorption of the adsorbed straight chain hydrocarbons from the adsorbent, conversion of the desorbed straight chain hydrocarbons into a mixture of straight Such Patented May l2, 1959 2 chain and non-straight chain hydrocarbons and recycle of this mixture to the adsorption step for the removal o f straight chain hydrocarbons from the mixture.

A petroleum fraction suitable for use in the practice of this invention might have an initial boiling point of about 40 F. and an end point of about 225 1F., more or less. Furthermore, such a petroleum fraction must contain both straight chain and non-straight chain hydro.- carbons and might have the following composition:

Hydrocarbon type: Percent by vol.

Any solid adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of nonstraight chain hydrocarbons can be employed in the practice of this invention. It is preferred, however, to employ as the adsorbent certain natural or synthetic zeolites or alumino-silicates such as a calcium alumino-silicate which exhibit the property of a molecular sieve, that is adsorbents made up of porous matter or crystals wherein the pores are of molecular diameter and are of uniform size. A particularly suitable solid adsorbent for the adsorption of straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons is Va. calcium alumino-silicate manufactured by Linde Air Products Company and designated Type 5A molecular sieve. The crystals of this particular calcium alumino-silicate, apparently actually a sodium calcium alumino-silicate, have a pore size or diameter of about 5 Angstrom units, a pore size suicient to admit straight chain hydrocar bons, such as the n-paralins, to the substantial exclusion of the non-straight chain hydrocarbons, such as the naphthenic, aromatic, iso-olenic and iso-paraflinic hydrocarbons, eg., isobutane and higher. This particular selec,- tive adsorbent is available in various sizes such as j,/16 and 1/s diameter pellets as well as in a finely-divided powder form.

Other selective adsorbents may be employed in the practice of this invention. For example, it is contemplated that selective adsorbents having the property `0f selectively adsorbing straight chain hydrocarbons to .the substantial exclusion of non-straight chain hydrocarbons in the manner of a molecular sieve may be obtained by suitable treatment of various oxide gels, especially `metal oxide gels of the polyvalent amphoteric metal oxides.

Other suitable selective adsorbents areknown and include the synthetic and natural zeolites which, when dehydrated, may be described as crystalline zeolites having a rigid three dimensional anionic network and having interstitial dimensions sulliciently large to adsorb straight chain hydrocarbons but suciently small to exclude the non-straight chain hydrocarbons. The naturally occurring zeolite, chabazite, exhibits such desirable properties. Another suitable naturally occurring yzeolite is analcite (NaAlSi2O6H2O) which, when dehydrated, andy when all or part of the sodium is replaced by an alkaline earth metal, such as calcium, yields a material which may be represented by the formula,(CaNa)Al2Si4O12.2H2O and which, after suitable conditioning, will adsorb straight chain hydrocarbons to the substantialexclusion of nonstraight chain hydrocarbons. Naturally occurring, or synthetically prepared phacolite, gmelinite, harmotome, and the like or suitable modications of these products by base exchange, are also applicable in the practice of this invention.

Other solid adsorbents which selectively adsorb straight chain hydrocarbons such as n-parans and n-olens to the substantial exclusion of non-straight chain hydrocarbons, including the aromatic and naphthenic hydrocarbons, are known.

The naphtha undergoing treatment for the removal of straight chain hydrocarbons therefrom may be present either in the liquid phase or gas or vapor phase. The capacity of the solid adsorbent as a selective adsorbent for straight chain hydrocarbons is substantially unaffected by the phase condition of the hydrocarbons in contact therewith, provided, of course, sufficient time is allowed to substantially saturate the adsorbent. It is preferred in the practice of the invention to maintain the naphtha in a vapor phase while in contact with the solid adsorbent. Contact of the naphtha with the adsorbent may be effected by any suitable means for effecting gas-solid or liquid-solid contacting and the selective adsorbent may be maintained as a fixed bed, a moving bed or a iiuent or uid bed of nely divided particles.

When liquid phase contacting is carried out for the removal of straight chain hydrocarbons from the naphtha, it is preferred to conduct the adsorption operation at a temperature in the range 50-500 F. or higher, sufficient pressure being applied, if necessary, to maintain the naphtha in the liquid phase. In vapor phase adsorption it is preferred to carry out the adsorption operation at a temperature at least sufficient to maintain substantially all of the naphtha undergoing treatment in the vapor phase, such as a temperature in the range Z50-700 F.

The naphtha undergoing treatment is desirably maintained in contact with the selective adsorbent until substantially all of the straight chain hydrocarbons have been removed therefrom or until the selective adsorbent has become substantially saturated with respect to straight chain hydrocarbons. When the adsorbent is substantially saturated, so that straight chain hydrocarbon adsorption is no longer possible, the naphtha fraction is contacted with fresh or regenerated adsorbent. The straight chain hydrocarbons are desorbed from the adsorbent, thereby regenerating the adsorbent, by contacting the adsorbent with a stripping medium which displaces or purges the adsorbed straight chain hydrocarbons from within the pores of the selective adsorbent. Exemplary of a suitable gaseous stripping medium are nitrogen, methane, hydrogen, flue gas, carbon dioxide, natural gas, propane, n-butane, isobutane, and steam, preferably superheated steam, or mixtures thereof. In general, any vaporized or gaseous material is suitable as a stripping medium provided it is readily separable by suitable means, as by fractionation, from the desorbed stragiht chain hydrocarbons. Desirably, when superheated steam is employed as the stripping medium, it is followed by another gaseous stripping medium such as an inert purge gas, e.g. methane, in order to sweep the steam from within the pores of the adsorbent.

The desorption operation can be carried out at any suitable temperature. A desorption temperature in the range 500-1 100 F. has been found to be satisfactory. Although the desorption temperature is usually G-300 F. higher than the adsorption temperature, such as a temperature in the range 700-1000 F., the desorption operation may be carried out at substantially the same temperature as the adsorption temperature. Desorption of the straight chain hydrocarbons may also be effected in the liquid phase by contacting the adsorbent with a polar liquid, e.g. water which is preferentially adsorbed over the straight chain hydrocarbons, at a suitable elevated temperature as indicated above.

After the straight chain hydrocarbons have been desorbed, they are recovered and subjected to a suitable conversion operation. Suitable conversion operations include catalytic reforming, aromatization, dehydrocyclization, isomerization and thermal cracking or reforming in order to upgrade the desorbed straight chain hydrocarbons into more valuable higher octane hydrocarbons. Preferably, the conversion operation is an isomerization operation employing an isomerization catalyst, such as a platinum-containing catalyst or an aromatization operation employing a chromia-containing catalyst.

Isomerization of the desorbed straight chain hydrocarbons is desirably eifected by contacting the desorbate with a platinum-containing catalyst, such as a U.O.Pr platforming catalyst. Isomerization may be conducted over a wide range of operating conditions. Suitable conversion temperatures range from 20G-900 F. more or less, preferably in the range 40G-800 F. The pressure may vary from 02000 F. p.s.i.g., a pressure in the range 50-750 being preferred. The space velocity of the hydrocarbon feed in the isomerization may range between 0.25 to 10 v./hr./v. and the hydrogen recycle rate from 500 to 10,000 cu. ft./bbl. of feed.

Isomerization or conversion of the desorbed straight chain hydrocarbons produces an upgraded mixture of straight chain and non-straight chain hydrocarbons. The mixture so produced is further upgraded by recycling it back to the adsorption step for the removal of straight chain hydrocarbons from the mixture. In this manner, the straight chain hydrocarbons are continuously removed and the treated and upgraded product issuing from the adsorber is substantially free of straight chain hydrocarbons.

Referring now to the drawing, there is schematically illustrated an embodiment of the practice of this invention. Referring to the drawing in detail, a light straight run naphtha boiling in the range 40 to 225 F. is introduced via line 10 to heater 11. In heater 11, the naphtha is brought up to a suitable temperature preparatory to the adsorption operation. From heater 11, the naphtha is passed via line 12 to adsorber 14. Adsorber 14 contains a bed of solid selective adsorbent, Linde Type 5A molecular sieve, for the adsorption of straight chain hydrocarbons. Conditions within the adsorber to effect the adsorption of straight chain hydrocarbons may range between temperatures of 200 to 700 F. and pressures from 0 to 600 p.s.i.g. After a suitable residence time within adsorber 14 to effect the adsorption of straight chain hydrocarbons, the naphtha, substantially free of straight chain hydrocarbons, is recovered via line 15 as a finished or treated product. To completely remove the treated naphtha from adsorber 14, the adsorber is purged with a stripping medium (which desirably is the same as the desorbing medium) to displace the treated naphtha from the adsorber. Effective stripping mediums include gases such as nitrogen, carbon dioxide, methane, hydrogen and the like. The stripping medium is introduced to adsorber 14 via lines 16, 18 and 12, as indicated in the drawing.

Following completion of the adsorption phase, the adsorbent is subjected to desorption to effect the removal of straight chain hydrocarbons therefrom, i.e. to regenerate the adsorbent. Suitable desorption conditions include temperatures in the range 500-1100 F., generally 100- 300 F. above adsorption temperatures, and pressures in the range 0-600 p.s.i.g. usually lower than the adsorption pressure. Isobaric and/or isothermal adsorption desorption conditions may be employed if desired.

Desorption is materially aided by the introduction of a gaseous desorbing medium which may consist of hydrogen, nitrogen, carbon monoxide, carbon dioxide, methane, flue gas, steam and others to strip the normal paraftins from the adsorbent. The desorbing medium is introduced via lines 2t), 18 and 12 into adsorber 14 and the resulting desorbed straight chain hydrocarbons admixed with the gaseous desorbing medium is carried via line 22 into converter 26.

Converter 26 may consist of any converter unit suitable for transforming straight chain hydrocarbons into branched chain or cyclic hydrocarbons. Converter 26 is desirably an isomerization unit packed with a fixed bed of platinum-containing isomerization catalyst. In converter 26, the straight chain hydrocarbons are contacted with th@ isomerization catalyst under isomerizing conditons of temperature and pressure. The straight chain hydrocarbons are converted into branched chain hydro# carbons of substantially the same carbon'content but of higher octane value. The effluent from converter 26,

Blending .0f `the treated naphtha and .theitreated isomate gives a blend having a research clear v octane number of about 83.

Another mixture of straight chain :hydrocarbons comwhich contains a mixture of straight chain and nonstraight parable to the hydrocarbons desorbed from the ksolid adchain hydrocarbons is passed via line 28 to liquid-gas sorbent and having a research clear octane number .of separator 30 to effect the removal of gaseous products about 3 9 was .contacted with a U. O.P. dehydrogenation formed within or carried into converter 26. Gaseous catalyst consisting of chrornic oxide,.magnesiumoxideand products are removed via line 37. The gaseous eluent aluminum oxide. The 4mixture of straight .chain hydroremoved via line 37 when containing a substantial amount 1 0 carbons was contained at a pressure of 40 4p.s.i.g. and .a of hydrogen, greater than 50 vol. percent, if desired, is space velocity of 0.4 v./hr./v. inthe presence of hydrogen advantageously employed as the stripping or desorbing atarecycle rate of ,1200 cu. ft/bbl. Contacting temperamedium "for adsorber 14 via 'lines 36, 38, 18 and 12, or tures and the .results obtained are given in Table I below: recycled directly to converter 26 via lines 3 6, 39, andl 221. The mixture of straight chain and non-.straight chain Table l hydrocarbons separated in liquid-gas separator 30 is passed via lines 31, 32 and 12 into adsorber 14 to effect the ad- Temperature, F 920 94a sorption of the straight chain lhydrocarbons from the treated product. VBy operating in .this manner, it is posysvclereelirit Recovery 93.28 812g sible to substantially completely remove straight chain 2 0 Imm 0 hydrocarbons from the treated product. If desired, the ioontilisd sois 5tlg mixture of straight chain and nonstraight chain hydro- +3 C@ TEL/gal 804 802 carbons maybe recycled to heater 11 via lines 31 and 34 in ord'er to 'bring the mixture to the proper temperature other mixtures of Straight chain :hydrocarbons `c0m PUOI t0 mtfOdPctlOn mto id sorbef 14- 25 parable to the straight chain hydrocarbons recovereddur- The. following example lllustrates the practice of this ing the desorption operation having compositions of mventlonabout 23% -by volume n-pentane, 5.6% by yvolume n- EXAMPLE I hexane and 21% by volume n-heptane and exhibiting a A light straight run naphtha ,havin-g a research clear research clear octane number of 39 were contacted with octane number -of about 69 and a. boiling range of 14.6- 30 various .catalysts Under A.isornerjzing AConditions including 226 F. was contacted with a sodium calcium aluminoa Pressure 0f 500 11S-Lg a Space Velocity 0f 1-0 V/h1'/V silicate adsorbent, Linde Type 5A molecular sieve, in the and a hydrogen reCyCle fate 0f 4000 CU- t-/bbl The following manner in accordance with our invention. The catalysts, reaction temperatures, and research clear octane naphtha was vaporized and maintained in the vapor phase 35 numbers of the converted products and of the nished at a temperature about 250 F. These vapors were products, i.e. converted products after having been conpassed over a fixed bed of adsorbent at a space velocity tacted with adsorbent for the removal of straight chain of about 0.5-1.0 v./hr./v. Fol-lowing the adsorption step, hydrocarbons, are set out in Table II below:

Table Il Temp., F 800 850 900 Catalyst Plat. Baker Ultra Plat. Baker Ultra Plat. Baker Ultra Liq. Ree., Wt. Percent 95.9 99.3 90.1 95.0 99.0 88.2 67.6 70.1 72.7 Converted Product, Octane No. 60. 0 51. 0 54.0 75. 4 74. 0 77. 1 89. 6 70.0 78. 9 Product Finished by Selective Adsorption, octane No 78.0 61.0 72.0 84.0 82.0 82.6 80.3

Plata-UCP platorming catalyst.

the treated naphtha, now substantially free of straight chain hydrocarbons, was tested Vand found to have a research clear octane number of about 83.7. The adsorbed hydrocarbons were recovered and found to tbe substantially normal paraflinic having a low octane number.

A mixture of straight chain hydrocarbons, comparable to the aforesaid straight chain hydrocarbons recovered during the desorption operation, having a composition of about 23% by volume normal pentane, 56% by volume normal hexane and 21% by volume normal heptane and exhibiting a research clear octane number of 39 was contacted with a platinum isomerization catalyst at a temperature about 850 F., a pressure of 500 p.s.i.g. and a space velocity of 1 v./hr./v. employing a hydrogen recycle rate of about 4000 standard cubic feet per barrel of charge. The resulting isomate was produced in 99 weight percent yield and consisted of a mixture of straight chain and nonstraight chain hydrocarbons having a research clear octane number of about 74. This isomate was vaporized and contacted with the solid selective adsorbent for the removal of straight chain hydrocarbons under conditions similar to those employed in treating the feed naphtha. The thus treated isomate exhibited a research clear octane number of about 82.0.

The foregoing example illustrates how a light naphtha may be treated to produce an upgraded light naphtha blending stock. The advantages of this process are apparent. Only the straight chain hydrocarbons are subjected to the hydrocarbon conversion step thereby increasing the branched chain hydrocarbon content of the total naphtha. Another advantage due to the recycle adsorption step from the converting operation is that the upgraded product is substantially free of the relatively low octane straight chain hydrocarbons.

This application is a continuation-impart of our copending patent application Serial No. 478,426, filed December 29, 1954.

Obviously, many modifications and changes may be made in the process of this invention without departing from the spirit or scope thereof, and therefore only those limitations should be imposed as are indicated in the appended claims.

We claim:

l. A process for treating a hydrocarbon fraction boiling in the range 40-225 F., said fraction containing straight chain and non-straight chain hydrocarbons, said straight chain hydrocarbons including n-hexane, n-heptane and -n-octane, said non-straight chain hydrocarbons com- 7 prisng isoparanic, naphthenic and aromatic hydrocarbons, which comprises contacting said fraction in the gaseous phase witha solid alumino-silicate molecular sieve adsorbent which selectively adsorb's straight chain hydrocarbons to the substantial 'exclusion of non-straight chain hydrocarbons to 'adsorb only the straight chain hydrocarbons from said fraction, desorbing the adsorbed straight chain hydrocarbons from said adsorbent by contact with gaseous hydrogen, isomerizing the resulting desorbed straight chain hydrocarbons in the presence of said hydrogen to form a mixture of straight chain and nonstraight chain hydrocarbons, separating said mixture from said hydrogen and recycling said mixture to contact said adsorbent for the removal of straight chain hydrocarbons from said mixture.

2. A process for treating a hydrocarbon fraction boiling in the range 40-225 F., said fraction containing straight chain and non-straight chain hydrocarbons, which comprises contacting said fraction in the gaseous phase with a solid alumino-silicate molecular sieve adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons to adsorb only the straight chain hydrocarbons from said naphtha, desorbing the adsorbed straight chain hydrocarbons from said adsorbent with gaseous hydrogen catalytically converting the resulting desorbed straight chain hydrocarbons in contact with said hydrogen into a mixture of straight chain and non-straight chain hydrocarbons, separating said mixture from said hydrogen, recycling said mixture of straight chain and non-straight chain hydrocarbons to contact said adsorbent and recycling said hydrogen to said catalytic converting operation and to the aforesaid desorption operation.

3. A process for treating a hydrocarbon fraction boiling in the range 40-225" F., said fraction containing straight chain and non-straight chain hydrocarbons, said straight chain hydrocarbons including n-hexane, n-heptane and n-octane, said non-straight chain hydrocarbons comprising isoparanic, naphthenic and aromatic hydrocarbons which comprises contacting said fraction in the gaseous phase with a solid alumino-silicate molecular sieve adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons to adsorb only the straight chain hydrocarbons from said naphtha, desorbing the adsorbed straight chain hydrocarbons from said adsorbent with gaseous hydrogen, catalytically converting said straight chain hydrocarbons in the presence of said hydrogen into a mixture of straight chain and non-straight chain hydrocarbons, separating said mixture from said hydrogen, recycling said mixture of straight chain and non-straight chain hydrocarbons to contact said adsorbent and recycling said hydrogen to said desorption operation.

References Cited in the le of this patent UNITED STATES PATENTS 2,425,535 Hibshman Aug. 12, 1947 2,522,426 Black Sept. 12, 1950 2,602,772 Haensel July 8, 1952 

1. A PROCESS FOR TREATING A HYDROCARBON FRACTION BOILING IN THE RANGE 40-225* F., SAID FRACTION CONTAINING STRAIGHT CHAIN AND NON-STRAIGHT CHAIN HYDROCARBONS, SAID STRAIGHT CHAIN HYDROCARBONS INCLUDING N-HEXANE, N-HEPTANE AND N-OCTANE, SAID NON-STRAIGHT CHAIN HYDROCARBONS COMPRISING ISOPARAFFNIC, NAPHTHENIC AND AROMATIC HYDROCARBONS, WHICH COMPRISES CONTACTING SAID FRACTION IN THE GASEOUS PHASE WITH A SOLID ALUMINO-SILICATE MOLECULAR SIEVE ADSORBENT WHICH SELECTIVELY ADSORBS STRAIGHT CHAIN HYDROCARBONS TO THE SUBSTANTIAL EXCLUSION OF NON-STRAIGHT CHAIN HYDROCARBONS TO ADSORB ONLY THE STRAIGHT CHAIN HYDROCARBONS FROM SAID FRACTION, DESORBING THE ADSORBED STRAIGHT CHAIN HYDROCARBONS FROM SAID ADSOBENT BY CONTACT WITH GASEOUS HYDROGEN, ISOMERIZING THE RESULTING DE- 